The present invention relates to a method for treating dust or sludge. As used herein, the term "dust" includes dusts and sludges from electric furnaces.
The major constituent of electric furnace dust is metal oxides such as iron, zinc, lead, chromium and cadmium. These metals ideally can be reused, but it is difficult to reuse them as furnace materials because they contain large amounts of zinc. Even when such dusts are used as reclamation materials, harmful metals such as chromium, cadmium and lead are prone to dissolution by rain water etc., so that various treatments are required to prevent the dissolution of harmful metals, which requires a lot of time.
Processes for treating electric furnace dust are disclosed by the present inventors in Japanese Publications of Examined Patent Applications No. SHO60-23870 and No. SHO60-28897. These techniques relate to a process in which electric furnace dust is introduced into a molten steelmaking slag, a molten reaction occurs utilizing the sensible heat of the slag, zinc and lead are recovered by volatilization and the remainder is recovered.
The inventors of the present invention have adopted conventional techniques and have achieved conventional results. However, it has been found that there is room to vastly improve those conventional techniques.
Molten steelmaking slag has enormous sensible heat, but the quantity of heat is deficient for the purpose of achieving a sufficient reaction and efficiently volatilizing zinc and lead.